The field of the present invention is wireless communication systems. More particularly, the present invention relates to dynamic RF power management for use with an ultra-wideband communication system.
Wireless communication systems are changing the way people work, entertain themselves, and communicate with each other. For example, the wide acceptance of mobile devices, such as the portable phone, has enabled great mobility while enabling easy voice and data communication with family, friends, and co-workers. As more features are added to these mobile wireless devices, users are able to receive a wider variety of information to facilitate enhanced entertainment and to more efficiently solve business problems. Data, such as computer files, graphics, video, and music may now be sent from a remote location and received at mobile wireless devices. Such wide area uses generally require a series of fixed transceivers arranged to communicate with the mobile wireless devices. In such a manner, the wireless device is enabled to communicate so long as the wireless device remains in contact with at least one of the fixed transceivers.
Not only is the use of such wide area systems expanding, but the use of local wireless communication systems is also growing. For example, wireless devices in a single building, such as a residence, may be configured to share information. Such local wireless communication systems may enable computers to control peripherals without physical connections, stereo components to communicate, and almost any appliance to have access to the Internet to send and receive information.
The amount of data being sent on both wide and local communication systems is mushrooming, and may quickly exceed the bandwidth available in the traditional communication bands. It has been recognized that a relatively new communication technology, xe2x80x9cultra-widebandxe2x80x9d may provide assistance in meeting the ever increasing bandwidth demands. For example, U.S. Pat. No. 6,031,862, entitled xe2x80x9cUltra-wideband Communication System and Methodxe2x80x9d, discloses a communication system using an impulse radio system. Impulse radio is a form of ultra-wideband communication using individually pulsed monocycles emitted at fractions of nanosecond intervals to transmit a digital signal. The pulses are transmitted at extremely low power density levels, for example, at less than xe2x88x9230 db to xe2x88x9260 dB. The generated pulses are so small that they typically exist in the noise floor of other more traditional communication systems.
An ultra-wideband communication system enables communication at a very high data rate, such as 100 megabit per second or greater, when operated in a small local area. However, since the ultra-wideband communication system needs to avoid interfering with the more established communication frequencies, the ultra-wideband system must operate at extremely low power, typically transmitting signals at the noise level. Accordingly, each ultra-wideband cell is severely restricted in size as compared to the more traditional continuous wave or carrier based systems.
Since each cell is so small in an ultra-wideband communication system, the system must have many fixed antenna sites to cover a geographic area. With so many antennae operating simultaneously, mobile transceivers are likely to be receiving communication signals from several transmitters including transmitters in adjacent cells and transmitters in more distant cells. With every cell potentially receiving signals from so many transmitters, communication channels must be geographically separated to minimize the occurrence of channel interference. For example, if a particular channel is used in cell, that channel may not be usable in any other cell within several miles. Accordingly, since only a relatively small subset of communication channels is available in each cell, the bandwidth of the overall communication system is substantially reduced.
Also, wireless communication systems suffer from a xe2x80x9cnear-farxe2x80x9d problem, where a near transmitter""s signal can overpower and saturate a receiver while a far transmitter""s signal may be too weak to be reliably received. Since an ultra-wideband communication system has so many antenna sites, the severity of the near-far problem is exacerbated.
In any known conventional cell, utilized bandwidth varies as a function of user demand. Since user demand can vary greatly from one time period to another, there are likely to be times when a particular cell is greatly under-utilized, and other times when that same cell is saturated, thereby causing undesirable drops in transmissions, connection refusals, and quality degradation. In conventional communication signals, when a cell""s bandwidth utilization exceeds system quality standards, the system operator typically will add another cell in the area to move some of the user traffic from the over-utilized cell to the new cell. However, adding cells and antennas can be a costly and time consuming process.
Although ultra-wideband has the ability to greatly decrease the impact of multipath interference, it is still subject to attenuation of the received signal as it traverses the distance between transmitter and receiver. For a point RF source, received signal strength varies as the inverse of the squared distance for open line of sight communications. In cluttered and mobile environments, the attenuation is more closely proportional to the inverse of the fourth power of the distance due to multipath cancellation, which is still present even in ultra-wideband signals. In either scenario, the attenuation of the signal can decrease the signal level to a value that is unsuitable for reliable data transfer. Due in part to the deficiencies described above, convention known ultra-wideband communication systems do not enable efficient utilization of bandwidth and system resources.
It is an object of the present invention to provide an ultra-wideband communications system that enables greater system efficiency and increases bandwidth utilization. To meet the stated objective, and to overcome the disadvantages in known communication systems, an ultra-wideband communication system is disclosed.
Briefly, the ultra-wideband communication system includes a transceiver configured to receive an ultra-wideband communication signal, which has embedded power level data. A measurement circuit in the transceiver measures the strength of the received signal. An attenuation factor is computed that compares the measured signal strength to the data embedded in the signal. An adaptive circuit uses the attenuation factor to select a power level for a next transmission. In a preferred configuration, the transceiver also has a positioning circuit that is used to accurately determine the distance from the transceiver to the source of the communication signal, and the adaptive circuit uses the distance to tune the power level for the next transmission.
Advantageously, the ultra-wideband communication signal enables accurate selection of power levels to optimize the efficiency of the communication system. More particularly, the accurate selection of the lowest acceptable power level minimizes interference between communication cells, thereby increasing reliability and optimizing bandwidth utilization.